The need to manage group calls within Radio Access Networks is becoming more prevalent as dispatch services are moving away from traditional two-way radio service to cellular, network, or enterprise network based services such as Wireless Local Area Network (WLAN) including Voice over Internet Protocol (VoIP) services and the like.
One problem facing management of a group call set up in a WLAN environment is the time that would be required to individually address each communication unit in a target list and to wait for individual connections to be established as targets join. Further complications arise if selective and/or conditional targeting is required. Thus, setting up and controlling group calls such as dispatch calls to large groups in a network such as a WLAN VoIP network requires using a broadcast address such as an IP multicast address to contact target communication units simultaneously.
Traditionally, the Session Announcement Protocol (SAP) has been used for group call set up and management purposes. Problems arise however with the use of SAP. For example, in a wireless environment SAP necessarily leads to excessive battery use since, under SAP, all communication units must inspect announcements of any and all group calls being initiated using SAP.
One approach is to use the Session Initiation Protocol (SIP) as more fully described in Internet Engineering Task Force (IETF) Request For Comments (RFC) 3261. However, traditional SIP messages can not be delivered to a call target using a multicast address. Also, responses to SIP messages can be verbose adding delay to call set-up and adding load to the network. It is well known that SIP can be used to set up a conference call using multicast, see, for example, RFC 3261, section 2, Overview of SIP Functionality. However, the multicast address is used only for the bearer portion of the conference call and not for broadcast of the SIP signaling messages. Other IETF documents, such as RFC 2543 and RFC 3261 discuss the use of SIP with a multicast address. However, a multicast address is only allowed for use when a SIP REGISTER message must be sent, for example in a case where a User Agent (UA) communication unit does not know how to find the SIP registrar (RFC 3261, section 10.2.6, Discovering a Registrar). In other SIP literature it has be suggested that a UA initiating a session can also send the initial INVITE to an ALL SIP SERVERS multicast address, in a case where the UA does not know how to find the proper SIP server. Such a method, aside from not being adopted for standards purposes, has drawbacks in that it fails to address the need to contact all participants of a group or target communication units associated with a group call.
In co-pending U.S. patent application Ser. No. 10/334,521 session control is described using a multicast address and a mixture of SIP and SAP. However, the above identified application fails to describe a system for managing and controlling group calls using SIP and a multicast address.
Therefore, to address the above described problems and other problems, what is needed is a method and apparatus for facilitating session control in a group call.